You can buy narrow spring perches for late model rear ends from many dealers like Jim Carter. I have a 78-81 Camaro rear end in my '39 GMC 1/2 Ton with stock springs.


1939 GMC AC-102 Long Bed 1/2-Ton
In the Legacy Stovebolt Gallery
More details in his DITY Bay

1940 Chevy WB Series 1.5-Ton
In the Stovebolt Gallery